Mixing apparatus

ABSTRACT

A mixing apparatus ( 100 ) for mixing at least two fluids, the mixing apparatus ( 100 ) comprising a shaft ( 120 ) rotatable about its longitudinal axis ( 121 ), a first ( 122 ) and a second ( 124 ) radially extending impeller mounted on the shaft ( 120 ) and respectively axially spaced apart, characterised in that the first impeller ( 122 ) comprises a plurality of curved blades ( 125 ) operable to move said fluids in an axial direction towards the second impeller ( 124 ), and the second impeller ( 124 ) comprises a plurality of curved blades ( 125 ) operable to move said fluids in an axial direction towards the first impeller ( 122 ).

The invention relates to a mixing apparatus. In particular, but not exclusively, the invention relates to an apparatus for dispersing gas in liquid.

Many industrial processes incorporate an impeller driven mixing system, for example, processes for fermentation, hydrogenation, chlorination, oxidation, and carbonylation.

Impeller driven mixing systems generally incorporate one impeller mounted on a rotating shaft. Such systems may be said to have an axial longitudinal flow parallel to the axis of the rotating shaft and/or a radial flow parallel to the radially extending blades mounted on the shaft. The impeller may thus be a radial flow impeller which projects fluid in a radial direction towards a wall of a chamber in which the impeller is housed, for example, a Chemineer BT-6™ turbine, or alternatively, the impeller may be an axial flow impeller which comprises radially extending blades that are pitched at an angle so as to direct the fluid flow in an axial direction. Examples of axial flow impellers include marine impellers and hydrofoil impellers. Mixed flow systems are known, where the impeller causes flow in both axial and radial directions. An example of a mixed flow impeller is the 45° pitched blade turbine. Such mixing systems can be used in liquid-liquid, liquid-solid, or liquid-gas reactions.

A dual impeller system for dispersing a gas in a liquid, in a vessel, is known. Specifically, in a paper by Kuboi, entitled “The Power Drawn by Dual Impeller Systems Under Gassed and Ungassed Conditions” Fourth European Conference on Mixing, Apr. 27-29 1982, the combination of two axially spaced 45° pitched blade turbines is disclosed whereby a first impeller is mounted below a second impeller on a common shaft. The impeller blades are orientated such that the first impeller projects liquid upwards and outwards and the second impeller projects liquid downwards and outwards. Under gassed conditions, as gas is introduced into the vessel, the first impeller causes the incoming flow of gas bubbles to split so that some of the flow is driven radially outwards towards the walls of the vessel, and some is driven axially upwards towards the second impeller.

The effectiveness of the two impeller system under gassing conditions depends upon the speed of rotation of the impellers. At lower speeds it is possible that the bubbles that have been projected upwards by the first impeller are not affected by the second impeller. The second impeller is unable to overcome buoyancy forces and therefore the second impeller plays no part in the dispersion of gas in the liquid only when the rotational speed of the second impeller is increased are the buoyancy forces overcome. Disadvantageously, non-uniform dispersion of the gas in the liquid results. This is shown in FIG. 1 of the application. In order to achieve uniform dispersion, further disadvantageously, the rotational speed of the second impeller has to be sharply increased.

It is highly desirable to be able to achieve complete uniform dispersion in an industrial process. In industrial processes where gas/liquid mass transfer is an essential feature, this aids controllability and enhances reactor performance. In such processes, when the gas is well dispersed, a region of reasonably uniform turbulent

kinetic eddy dissipation can exist in the liquid between and around the impellers which controls coalescence and breakup of the bubbles. If the gas dispersion is highly non-uniform, undesirable coalescence can result in a sharp increase in bubble size and therefore, the surface area for interface mass transfer to occur is reduced. Advantageously, a controlled turbulent kinetic energy dissipation field results in a narrow bubble size distribution over a range of impeller specific powers.

It is an object of the present invention to provide a mixing apparatus which enables controllable mixing of fluids or solids whilst simultaneously providing an effective mixing environment.

According to a first aspect of the present invention there is provided a mixing apparatus for mixing at least two fluids, the mixing apparatus comprising a shaft rotatable about its longitudinal axis, a first and a second radially extending impeller mounted on the shaft and respectively axially spaced apart, characterised in that the first impeller comprises a plurality of curved blades operable to move said fluids in an axial direction towards the second impeller, and the second impeller comprises a plurality of curved blades operable to move said fluids in an axial direction towards the first impeller.

Preferably, the blades on each impeller are inward pumping into the space between the impellers. In the case of a substantially vertical shaft, the lower impeller is, therefore, upward pumping and the upper impeller is downward pumping. Preferably, the blades of each impeller are hydrofoil blades. A suitable hydrofoil blade is the Chemineer Maxflo™ W. Alternatively, the Lightnin A315™, A320™ or A340™ may be used.

Advantageously, due to the opposing axial flows created by the first impeller and the second impeller, a region of high turbulence is observed in a central mixing zone between said impellers. The high turbulence is maintained in this zone, and so there is little variation in the turbulence energy dissipation. Consequently, there is minimal variation in bubble size which results in a narrow size distribution of the bubbles in the central mixing zone. Advantageously, a narrow bubble size distribution enables the process or chemical reaction to be more easily controlled. This region provides a zone where the at least two fluids are brought together to be mixed. A chemical reaction can therefore be facilitated in the central mixing zone. The fluids may be liquid-solid, liquid-liquid, or liquid-gas. Preferably, the at least two fluids comprise a liquid and a gas.

It is advantageous to provide a gas/liquid mixing environment where the bubble size is largely independent of the impeller specific power. In such a system the liquid mixing time may be varied independently of the bubble size.

Preferably, the first impeller and the second impeller each comprise two or more curved blades, more preferably, three or more curved blades. Most preferably, are impellers with four curved blades. The provision of an impeller with a large number of curved blades increases the shear forces acting to break up large bubbles. The small bubbles produced have a smaller average bubble diameter than those produced with a first impeller and/or a second impeller with fewer curved blades and therefore, the available surface area for a reaction to occur is increased.

Preferably, the diameter of the first impeller is the same as the diameter of the second impeller. Preferably, the diameter of the or each impeller is substantially half the diameter of the vessel in which said impeller is mounted.

Advantageously, the smaller the diameter of the impeller, the greater the shear force created for a given power and therefore, a large number of small bubbles are produced which leads to an increase in available surface area for a reaction to occur.

Preferably, the axial distance between the first impeller and the second impeller is at least one impeller diameter apart. In this configuration, the turbulence created by the opposing impellers is an equilibrium in the central mixing zone which allows for prediction of bubble size and therefore control of the reaction occurring.

It is preferable that the total power drawn by the combination of impellers is low. Preferably, the impellers operate at a low power number, preferably substantially between 1 to 5, more preferably, substantially between 1 to 3, most preferably substantially 1.75. In so doing, the system consumes less energy than conventional systems which operate at power numbers of typically 3.2. The power may be measured using conventional equipment, for example, strain gauges.

Preferably, when operating at a low power number complete uniform dispersed phase distribution is achieved. This is highly desirable and is because of the energy efficiency of the blades, preferably hydrofoil blades.

Without being restricted by theory, one possible explanation for the efficiency of the invention is that the use of hydrofoil blades reduces tip vortices and converts more of the shaft energy into flow rather than turbulent kinetic energy, aiding complete dispersion.

Preferably, the specific power used when the first impeller and the second impeller rotate is substantially between 50 W/m³ to 900 W/m³, more preferably, substantially between 100 W/m³ to 800 W/m³.

Preferably, when dual opposed Maxflo type impellers are used in the system, the preferred specific power is substantially between 50 W/m³ to 900 W/m³. Preferably, when BT-6 type impellers are used, the preferred specific power is substantially between 400 W/m³ to 3200 W/m³. At such specific powers, a narrow bubble size distribution is maintained and the reaction is controlled.

Preferably, when dual opposed Maxflo impellers are used, the arithmetic mean size (d₁₀) is substantially between 250 μm to 550 μm and the surface volume mean diameter (d₃₂) is substantially between 400 μm to 750 μm. Preferably, when operating at substantially 750 rpm, the d₁₀ is substantially between 250 μm to 350 μm, most preferably substantially 296 μm, and preferably, the d₃₂ is substantially between 400 μm to 500 μm, most preferably substantially 450 μm. Preferably, when operating at substantially 991 rpm, the d₁₀ is substantially between 300 μm to 400 μm, most preferably substantially 330 μm, and preferably, the d₃₂ is substantially between 460 μm to 560 μm, most preferably substantially 510 μm. Preferably, when operating at substantially 1200 rpm, the d₁₀ is substantially between 350 μm to 450 μm, most preferably substantially 394 μm, and preferably, the d₃₂ is substantially between 450 μm to 550 μm, most preferably substantially 500 μm.

Preferably, when BT-6 type impellers are used, the d₁₀ is substantially between 250 μm to 1500 μm. Particularly, when operating at substantially 250 μm, preferably the d₁₀ is substantially between 550 μm to 650 μm, most preferably substantially 633 μm, and the d₃₂ is preferably substantially between 800 μm to 100 μm, most preferably substantially 978 μm. Preferably, when operating at substantially 380 rpm, the d₁₀ is preferably substantially between 800 μm to 900 μm, most preferably substantially 841 μm, and the d₃₂ is preferably substantially between 1000 μm to 1500 μm, most preferably substantially 1345 μm. At substantially 500 rpm, the d₁₀ is preferably substantially between 500 μm to 600 μm, most preferably substantially 597 μm, and the d₃₂ is preferably substantially between 700 μm to 800 μm, most preferably substantially 72 μm. Preferably, when operating at substantially 765 rpm, the d₁₀ is preferably substantially between 300 μm to 400 μm, most preferably substantially 378 μm, and the d₃₂ is preferably substantially between 400 μm to 500 μm, most preferably substantially 445 μm.

In a reactor where gas is sparged into an agitated liquid medium, preferably, the sparged gas rate is substantially between 0.05 to 1.0 m³/s, preferably substantially between 0.1 to 0.5 m³/s, most preferably substantially 0.13 m³/s at an impeller speed of preferably between 50 rpm to 1200 rpm, most preferably substantially 50 rpm to 200 rpm.

A key parameter used in the design of gas-liquid mixing systems is the critical dispersion speed. This is the minimum impeller speed required to ensure uniform dispersion of the gas bubbles. The critical dispersion speed for achieving dispersion in a dual opposed flow hydrofoil system in a vessel having a diameter of preferably substantially between 1 to 10 m, more preferably, substantially between 2 to 5 m, is preferably substantially between 1 to 100 rpm, preferably substantially between 5 to 50 rpm, more preferably substantially between 10 to 20 rpm, most preferably substantially 14 rpm.

Accordingly, in a further aspect of the present invention there is provided a chemical reaction system comprising a liquid phase and a mixing apparatus according to the first aspect of the invention for mixing a fluid into the liquid phase. Preferably, the fluid is a solid or most preferably, the fluid is a gas.

Preferably, the liquid phase comprises at least one liquid phase reactant for reacting with a gas introduced into the liquid phase, as well as at least one liquid phase reaction product. Preferably, the liquid phase includes a gas introduced therein. Preferably, the said gas comprises one or more reactants capable of reacting with the said one or more reactants. Preferably, the liquid phase comprises a catalyst system. Preferably, the reaction system is a carbonylation reaction system such as one described in co-pending United Kingdom patent application GB 0516556.8 or as referred to in European patents and patent applications EP-A-0055875, EP-A-04489472, EP-A-0106379, EP-A-0235864, EP-A-0274795, EP-A-0499329, EP-A-0386833, EP-A-0441447, EP-A-0489472, EP-A-0282142, EP-A-0227160, EP-A-0495547, EP-A-0495548, EP-A-1651587, EP-A-1565425, EP-A-1554039, EP-A-1534427, EP-A-1527038, EP-A-1204476, WO2005118519 and WO2005079981.

Preferably, the reaction system is a carbonylation process comprising carbonylating an ethylenically unsaturated compound with carbon monoxide in the presence of a source of hydroxyl groups, preferably, methanol, and a catalyst system comprising (a) a bidentate phosphine, arsine or stibine ligand, and (b) a catalytic metal selected from a group 8, 9 or 10 metal or a compound thereof, preferably palladium. Preferably, the phosphine ligand is selected from 1,2-bis-(di-tert-butylphosphinomethyl)benzene, 1,2-bis-(di-tert-pentylphosphinomethyl)benzene, 1,2-bis-(di-tert-butylphosphinomethyl)naphthalene, 1,2bis(diadamantylphosphinomethyl)benzene, 1,2bis(di-3,5-dimethyladamantylphosphinomethyl)benzene, 1,2bis(di-5-tert-butyladamantylphosphinomethyl)benzene, 1,2bis(1-adamantyl tert-butyl-phosphinomethyl)benzene, 1-(diadamantylphosphinomethyl)-2-(di-tert-butylphosphinomethyl)benzene, 1-(di-tert-butylphosphinomethyl)-2-(dicongressylphosphinomethyl)benzene, 1-(di-tert-butylphosphinomethyl)-2-(phospha-adamantyl-P-methyl)benzene, 1-(diadamantylphosphinomethyl)-2-(phospha-adamantyl-P-methyl)benzene, 1-(tert-butyladamantylphosphinomethyl)-2-(di-adamantylphosphinomethyl)benzene and 1-[(P-(2,2,6,6,-tetra-methylphosphinan-4-one)phosphinomethyl)]-2-(phospha-adamantyl-P-methyl)benzene, wherein “phospha-adamantyl” is selected from 2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxadamantyl, 2-phospha-1,3,5-trimethyl-6,9,10-trioxadamantyl, 2-phospha-1,3,5,7-tetra(trifluoromethyl)-6,9,10-trioxadamantyl or 2-phospha-1,3,5-tri(trifluoromethyl)-6,9,10-trioxadamantyl; 1,2-bis-(dimethylaminomethyl)ferrocene, 1,2-bis-(ditertbutylphosphinomethyl)ferrocene, 1-hydroxymethyl-2-dimethylaminomethylferrocene, 1,2-bis-(ditertbutylphosphinomethyl)ferrocene, 1-hydroxymethyl-2,3-bis-(dimethylaminomethyl)ferrocene, 1,2,3-tris-(ditertbutylphosphinomethyl)ferrocene, 1,2-bis-(dicyclohexylphosphinomethyl)ferrocene, 1,2-bis-(di-iso-butylphosphinomethyl)ferrocene, 1,2-bis-(dicyclopentylphosphinomethyl)ferrocene, 1,2-bis-(diethylphosphinomethyl)ferrocene, 1,2-bis(di-isopropylphosphinomethyl)ferrocene, 1,2-bis-(dimethylphosphinomethyl)ferrocene, 1,2-bis-(di-(1,3,5,7-tetramethyl-6,9,10-trioxa-2-phospha-adamantylmethyl))ferrocene, 1,2-bis-(dimethylaminomethyl)ferrocene-bismethyliodide, 1,2-bis(dihydroxymethylphosphinomethyl)ferrocene, 1,2-bis(diphosphinomethyl)ferrocene, 1,2-bis-α,α-(P-(2,2,6,6,-tetramethylphosphinan-4-one))dimethylferrocene, and 1,2-bis-(di-1,3,5,7-tetramethyl-6,9,10-trioxa-2-phospha-adamantylmethyl))benzene; cis-1,2-bis(di-t-butylphosphinomethyl)-4,5-dimethyl cyclohexane; cis-1,2bis(di-t-butylphosphinomethyl)-5-methylcyclopentane; cis-1,2-bis(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-4,5-dimethylcyclohexane; cis-1,2-bis(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl) 5-methylcyclopentane; cis-1,2-bis(di-adamantylphosphinomethyl)-4,5 dimethylcyclohexane; cis-1,2-bis(di-adamantylphosphinomethyl)-5-methyl cyclopentane; cis-1-(P,P adamantyl, t-butyl phosphinomethyl)-2-(di-t-butylphosphinomethyl)-4,5-dimethylcyclohexane; cis-1-(P,P adamantyl, t-butyl phosphinomethyl)-2-(di-t-butylphosphinomethyl)-5-methylcyclopentane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(di-t-butylphosphinomethyl)-4,5-dimethylcyclohexane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(di-t-butylphosphinomethyl)-5-methyl cyclopentane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(diadamantylphosphinomethyl)-5-methyl cyclohexane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(diadamantylphosphinomethyl)-5-methyl cyclopentane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(diadamantylphosphinomethyl)cyclobutane; cis-1-(di-t-butylphosphinomethyl)-2-(diadamantylphosphinomethyl)-4,5-dimethyl cyclohexane; cis-1-(di-t-butylphosphinomethyl)-2-(diadamantylphosphinomethyl)-5-methyl cyclopentane; cis-1,2-bis(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-4,5-dimethyl cyclohexane; cis-1,2-bis(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-5-methyl cyclopentane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(di-t-butylphosphinomethyl)-4,5-dimethyl cyclohexane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(di-t-butylphosphinomethyl)-5-methyl cyclopentane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(diadamantylphosphinomethyl)-4,5-dimethyl cyclohexane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(diadamantylphosphinomethyl)-5-methyl cyclopentane; cis-1,2-bis-perfluoro(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo{3.3.1.1[3.7]}-decyl)-4,5-dimethyl cyclohexane; cis-1,2-bis-perfluoro(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo{3.3.1.1[3.7]}decyl)-5-methyl cyclopentane; cis-1,2-bis-(2-phospha-1,3,5,7-tetra(trifluoro-methyl)-6,9,10-trioxatricyclo{3.3.1.1[3.7]}decyl)-4,5-dimethyl cyclohexane; cis-1,2-bis-(2-phospha-1,3,5,7-tetra(trifluoro-methyl)-6,9,10-trioxatricyclo{3.3.1.1 [3.7]}decyl)-5-methyl cyclopentane; cis-1,2-bis(di-t-butylphosphinomethyl)cyclohexane; cis-1,2-bis(di-t-butylphosphinomethyl)cyclopentane; cis-1,2-bis(di-t-butylphosphinomethyl)cyclobutane; cis-1,2-bis(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)cyclohexane; cis-1,2-bis(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)cyclopentane; cis-1,2-bis(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)cyclobutane; cis-1,2-bis(di-adamantylphosphinomethyl)cyclohexane; cis-1,2-bis(di-adamantylphosphinomethyl)cyclopentane; cis-1,2-bis(di-adamantylphosphinomethyl)cyclobutane; cis-1-(P,P-adamantyl, t-butyl-phosphinomethyl)-2-(di-t-butylphosphinomethyl)cyclohexane; cis-1-(P,P-adamantyl, t-butyl-phosphinomethyl)-2-(di-t-butylphosphinomethyl)cyclopentane; cis-1-(P,P-adamantyl, t-butyl-phosphinomethyl)-2-(di-t-butylphosphinomethyl)cyclobutane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(di-t-butylphosphinomethyl)cyclohexane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(di-t-butylphosphinomethyl)cyclopentane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(di-t-butylphosphinomethyl)cyclobutane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(diadamantylphosphinomethyl)cyclohexane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(diadamantylphosphinomethyl)cyclopentane; cis-1-(2-phosphinomethyl-1,3,5,7-tetramethyl-6,9,10-trioxa-adamantyl)-2-(diadamantylphosphinomethyl)cyclobutane; cis-1-(di-t-butylphosphinomethyl)-2-(diadamantylphosphinomethyl)cyclohexane; cis-1-(di-t-butylphosphinomethyl)-2-(diadamantylphosphinomethyl)cyclopentane; cis-1-(di-t-butylphosphinomethyl)-2-(diadamantylphosphinomethyl)cyclobutane; cis-1,2-bis(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)cyclohexane; cis-1,2-bis(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)cyclopentane; cis-1,2-bis(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)cyclobutane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(di-t-butylphosphinomethyl)cyclohexane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(di-t-butylphosphinomethyl)cyclopentane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]1}decyl)-2-(di-t-butylphosphinomethyl)cyclobutane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(diadamantylphosphinomethyl)cyclohexane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]})decyl)-2-(diadamantylphosphinomethyl)cyclopentane; cis-1-(2-phospha-1,3,5-trimethyl-6,9,10-trioxatricyclo-{3.3.1.1[3.7]}decyl)-2-(diadamantylphosphinomethyl)cyclobutane; cis-1,2-bis-perfluoro(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo{3.3.1.1[3.7]}-decyl)cyclohexane; cis-1,2-bis-perfluoro(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo{3.3.1.1[3.7]}decyl)cyclopentane; cis-1,2-bis-perfluoro(2-phospha-1,3,5,7-tetramethyl-6,9,10-trioxatricyclo{3.3.1.1[3.7]}decyl)cyclobutane; cis-1,2-bis-(2-phospha-1,3,5,7-tetra(trifluoro-methyl)-6,9,10-trioxatricyclo{3.3.1.1[3.7]}decyl)cyclohexane; cis-1,2-bis-(2-phospha-1,3,5,7-tetra(trifluoro-methyl)-6,9,10-trioxatricyclo{3.3.1.1[3.7]}decyl)cyclopentane; and cis-1,2-bis-(2-phospha-1,3,5,7-tetra(trifluoro-methyl)-6,9,10-trioxatricyclo{3.3.1.1[3.7]}decyl)cyclobutane; (2-exo, 3-exo)-bicyclo[2.2.1]heptane-2,3-bis(di-tert-butylphosphinomethyl) and (2-endo, 3-endo)-bicyclo[2.2.1]heptane-2,3-bis(di-tert-butylphosphinomethyl).

The bubble size produced by the invention may be small and therefore a large surface area is provided for interface mass transfer to take place. Furthermore, because the bubble size distribution is narrow with small deviation, the carbonylation reaction can be controlled.

All of the features described herein may be combined with any of the above aspects, in any combination unless such combinations are mutually exclusive.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic sectional side view of a prior art mixing apparatus;

FIG. 2 is a schematic sectional side view of a mixing apparatus according to the invention;

FIG. 3 is a schematic sectional side view of a mixing apparatus according to the invention in use; and

FIG. 4 is a further schematic sectional side view of a mixing apparatus according to the invention in use.

FIG. 1 shows a prior art mixing apparatus 10 in use in a vessel 12 containing a liquid 14. The vessel 12 has an inlet 16 through which a gas 18 is sparged into the liquid 14. The mixing apparatus 10 comprises a vertical elongate shaft 20 rotatable about a longitudinal axis 21 on which are fixedly mounted a first impeller 22 and a second impeller 24 in spaced apart relation. The first impeller 22 is mounted above the second impeller 24. Both the first and the second impellers 22,24 are 45° pitched blade turbines.

In use, said impellers must rotate at the same speed. The first impeller 22 causes incoming gas bubbles 26 to flow in a both an axial and radial direction. The axial component of the flow creates momentum, which along with buoyancy, prevents the second impeller 24 from operating effectively. The momentum and buoyancy is only overcome by increasing the speed of the impellers 22, 24. This increase in speed causes full dispersion of the gas 18 in the liquid 14 as shown in FIG. 1 by the lines A. Non-uniform dispersion of the liquid 14 in the gas 18 is undesirable because the mixing process cannot be controlled.

FIG. 2 shows a mixing apparatus 100 according to the present invention. The mixing apparatus 100 comprises a vertical elongate shaft 120 rotatable about a longitudinal axis 121 on which are fixedly mounted a first impeller 122 and a second impeller 124 in a spaced apart arrangement. Both the first and the second impeller 122, 124 comprise a number of hydrofoil blades 125. Each impeller 122,124 comprises four radially extending blades 125 fixedly mounted on the shaft 120 for co-operating rotation about the longitudinal axis of the shaft, in use. Each blade 125 on each impeller 122,124 is a hydrofoil blade arranged so as to impel the surrounding fluid axially in the direction of the other impeller. The first or lower impeller 122 is thus an up-pumping impeller and the second or upper impeller 124 is a down-pumping impeller.

Although only two blades 125 can be seen in the figure, it will be understood by a skilled person, that any number of blades may be used on each of the said impellers, for example, 3, 4 or even 6 blades. Particularly suitable commercially available impellers are those known as Maxflo™ W, A315, A320 or A340 impellers.

The first impeller 122 is mounted on the shaft 120 so that the concave face of the blades 125 face in an upward direction. The second impeller 124 is spaced along the shaft 120 and is mounted so that the concave face of the blades 125 face in a downwards direction. The distance between the first impeller 122 and the second impeller 124 is approximately the diameter of either of the said impellers 122, 124.

FIG. 3 shows the mixing apparatus 100 in a cylindrical vessel 112. A gas inlet 116 is located in the bottom-wall 132 of the vessel 112 adjacent to the base 132. It will be appreciated that the vessel 112 can be of any suitable alternative configuration, for example, it may be a hopper. The mixing apparatus 100 is centrally suspended in the vessel 112.

Although only one mixing apparatus 100 is shown in FIG. 3, it will be appreciated that any number of mixing apparatus 100 could be used in the chamber 112. For example, two, three, or four mixing apparatus 100 may be mounted in the chamber 112.

It will also be understood that any number of first or second impellers 122,124 may be mounted on the shaft 120 and in keeping with the object of the invention. For example, the arrangement 200 shown in FIG. 4, wherein a series of first impellers 222 and a series of second impellers 224 are mounted on the shaft 220. Any number of impellers 222,224 may be provided on the shaft 220.

An alternative configuration would comprise pairs of impellers mounted on the shaft. Each pair would comprise a first impeller and a second impeller. There may be a number of pairs of impellers on any given shaft, for example, two, three, or four pairs. In such an arrangement, the fluid, for example, gas, may be introduced into the chamber through the base or the side wall thereof, being directed under and towards the first impeller.

The first or the second impeller may be driven by a separate drive means so that the rotational speed of, for example, the first impeller, may be different to the rotational speed of the said other impeller.

The diameter of the first and second impellers may not necessarily be the same in any one of the embodiments shown. Further, the optimum distance between two impellers is dependent upon the geometry of the vessel and the diameter of said impellers.

In use, as in the illustrated carbonylation reaction, the vessel 112,212 is filled with fluid 114,214. A gas 118,218 is then directed into the vessel 112,212 via gas inlet 116,216. The shaft 120,220 is rotated by a suitable drive means (not shown), so as to cause the first impeller 122,222 and the second impeller 124,224 to rotate about the longitudinal axis 121,221 of the shaft 120,220 in a liquid 114.

The gas 118,218 enters the vessel 112,212 as large bubbles 150,215. Rotation of the first impeller 122,222 causes the large bubbles 150,215 to move in an axial direction towards the blades 125,225. The large bubbles 150,250 impact on the blades 125,225 and are broken up into a number of small bubbles 152,252 in the region of high turbulent energy dissipation. Small bubbles follow the liquid flow path which is initially axial then radial.

The second impeller 124,224 causes axial flow in a downwards direction towards the first impeller 122,222. Due to the opposing axial flow paths created by said impellers, a central zone 160,260, or high turbulent energy dissipation zone, is established. The central zone 160,260 comprises an area of comparatively uniform high turbulent energy dissipation with high interfacial area to allow reaction between reactants in the liquid 114,214 and in reactants in the gas 118,218. Further, because the turbulent energy dissipation in the central zone 160,260 is maintained without much variation, a narrow size distribution of small bubbles is produced. Such a narrow size distribution enables the reactor performance to be predicted and controlled.

The mixing apparatus 100,200 is particularly suited to carbonylation processes.

Table 1 gives an example of resultant bubble size for a dual opposed Maxflo impeller system operating at various speeds, and at 4.2 mm/sec. The bubble size was determined using a typical image capture camera.

TABLE 1 N (rpm) 750 991 1200 d₁₀ (μm) 296 330 394 d₃₂ (μm) 450 510 500

It is a distinct advantage to be able to control the reaction occurring between two fluids, particularly a liquid and a gas. It is also especially favorable to be able to promote effective and efficient mixing and interphase mass transfer between at least two fluids. When applied to industrial processes, such advantages are of high commercial value.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 

1. A mixing apparatus for mixing at least two fluids, the mixing apparatus comprising a shaft rotatable about its longitudinal axis, a first and a second radially extending impeller mounted on the shaft and respectively axially spaced apart, the first impeller comprising a plurality of curved blades operable to move said fluids in an axial direction towards the second impeller, and the second impeller comprising a plurality of curved blades operable to move said fluids in an axial direction towards the first impeller, characterised in that the at least two fluids comprise a liquid and a gas.
 2. A mixing apparatus as claimed in claim 1, characterised in that the blades on each impeller are inward pumping into the space between the impellers.
 3. (canceled)
 4. A mixing apparatus as claimed in claim 1, characterised in that the first impeller and the second impeller each comprise two or more curved blades.
 5. A mixing apparatus as claimed in claim 1, characterised in that the diameter of the first impeller is the same as the diameter of the second impeller.
 6. A mixing apparatus as claimed in claim 1, characterised in that the axial distance between the first impeller and the second impeller is at least one impeller diameter apart.
 7. A mixing apparatus as claimed in claim 1, characterised in that said impellers operate at a power number substantially 1.75.
 8. A mixing apparatus as claimed in claim 1, characterised in that the specific power used when the first impeller and the second impeller rotate is substantially between 100 W/m³ to 800 W/m³.
 9. A mixing apparatus as claimed in claim 1, characterised in that when dual opposed Maxflo impellers are used, the arithmetic mean size (d₁₀) is substantially between 250 μm to 550 μm and the surface volume mean diameter (d₃₂) is substantially between 400 μm to 750 μm.
 10. A mixing apparatus as claimed in claim 1, characterised in that when BT-6 type impellers are used, the d₁₀ is substantially between 250 μm to 1500 μm.
 11. A mixing apparatus as claimed in claim 10, characterised in that when operating at substantially 765 rpm, the d₁₀ is substantially 378 μm, and the d₃₂ is substantially 445 μm.
 12. A mixing apparatus as claimed claim 1, characterised in that the sparged gas rate is substantially between 0.05 to 1.0 m³/s.
 13. A mixing apparatus as claimed in claim 12, characterised in that the sparged gas rate is substantially 0.13 m³/s at an impeller speed of substantially 50 rpm to 200 rpm.
 14. A mixing apparatus as claimed in claim 1, characterised in that a critical dispersion speed in a vessel having a diameter of substantially between 2 to 5 m, is substantially between 10 to 20 rpm.
 15. A chemical reaction system comprising a liquid phase and a mixing apparatus according to the first aspect of the invention for mixing a fluid into the liquid phase.
 16. A chemical reaction system as claimed in claim 15, characterised in that the liquid phase comprises at least one liquid phase reactant for reacting with a gas introduced into the liquid phase, as well as at least one liquid phase reaction product.
 17. A chemical reaction system as claimed in claim 15, characterised in that the liquid phase comprises a catalyst system.
 18. A chemical reaction system as claimed in claim 15, characterised in that the reaction system is a carbonylation process comprising carbonylating an ethylenically unsaturated compound with carbon monoxide in the presence of a source of hydroxyl groups, and a catalyst system comprising (a) a bidentate phosphine, arsine or stibine ligand, and (b) a catalytic metal selected from a group 8, 9 or 10 metal or a compound thereof.
 19. A mixing apparatus substantially as hereinbefore described with reference to any one of the accompanying drawings. 